The answer is 605.
To find the average rate of change, we use the formula
[tex]A(x)=\frac{f(b)-f(a)}{b-a}[/tex]
For the interval [4, 6] we would use
[tex]7500=\frac{15605-x}{6-4}
\\
\\ 7500=\frac{15605-x}{2}[/tex]
Multiply both sides by 2:
7500*2 = 15605 - x
15000 = 15605 - x
Subtract 15605 from both sides:
15000-15605 = 15605-x-15605
-605 = -x
Divide both sides by -1:
-605/-1 = -x/-1
605 = x
